Pitot pumps are often used when fluids at high pressures and low flow rates are to be delivered to a utilization device. Pitot pumps are more efficient than other types of centrifugal pumps due to lower drag losses encountered during operation. Conventional pitot pumps utilize a fixed probe having an inlet comprising a hole disposed in a tip of the probe and an outlet wherein the cross-sectional area of the probe flow path increases from the inlet to the outlet The probe tip is disposed in a body of rotating fluid within a rotating housing such that the hole faces the flow of rotating fluid. The fluid is diffused after entering the probe to convert dynamic pressure into static pressure.
The outlet pressure or flow of a pitot pump can be controlled in one or a combination of two ways. Firstly, the speed of the prime mover that drives the pump can be controlled so that the velocity of the rotating body of fluid is in turn controlled. Since outlet pressure is related to the square of the velocity of the rotating body, it follows that outlet pressure can be controlled in this fashion. However, this technique can only be used where the speed of the prime mover can be adjusted to provide the desired pump output conditions. In applications such as in aircraft where a jet engine drives the pitot pump that in turn pumps fuel to a combustor of the jet engine, the speed of the jet engine varies in response to engine power requirements which do not match pump output requirements, and hence this flow control method is not available under most circumstances.
An alternative to the foregoing technique utilizes a throttling device or other flow control device that modulates the flow of pressurized fluid from the pump. However, such flow control devices are inefficient and convert energy into heat that in turn undesirably raises the temperature of the fluid.
Italian Patent 409,130 discloses a device having a movable pitot probe. No apparatus or device is shown for controlling the probe movement, however.
French Patent 924,143 discloses a device having a plurality of probes each of which appears to be movable. However, as with the Italian Patent noted above, no apparatus or device is shown for controlling the movement of the probes.
Erickson, U.S. Pat. No. 3,994,618 discloses a multiple outlet pitot pump that produces different output flows and/or pressures. A plurality of pitot tubes are disposed in the path of a rotating body of fluid. The pitot tubes are disposed at differing distances from the axis of rotation of the body of fluid. The tubes deliver fluid to discharge ducts at different flow rates.
Fottinger, U.S. Pat. No. 2,124,941 discloses a movable pick-up tube with a hydrodynamic shoe that keeps the pick-up tube submerged under a liquid-air interface in a partially filled scoop pump. However, the movement of the pick-up tube is not controlled to vary pressure or flow output.
Gurley, U.S. Pat. No. 1,722,289 discloses a two chamber pitot pump having a pitot probe in each chamber. The pitot probes, however, are not movable.
Blain, U.S. Pat. No. 4,549,861, assigned to the assignee of instant application, discloses a positive displacement machine having a pitot pickup tube which is movable for ease of assembly. In operation, the pitot tube remains stationary.